Friction lining

ABSTRACT

A friction lining, which has a friction part and a backing part. As a preform, wound from a strand material and treated with a binder, the friction part is subjected to hot pressing. It is suggested that the backing part is subjected to hot pressing together with the preform, so that a bond is created between the friction part and the backing part by the polymerization of the hinder.

The invention relates to a friction lining and also to a process forproducing a friction lining, in particular for clutch disks, comprisinga friction part of wound strand material and a carrier part.

Friction linings of this type are used, in particular, for clutch disksof friction clutches in motor vehicles, a frictional lock betweenmetallic friction surfaces of the friction clutch and the frictionlinings which, depending on the mode of operation of the frictionclutch, can adhere or slip and transmits a corresponding torque from adrive unit to an output.

Owing to the high rotational speeds of the friction clutch, the frictionlining is to have a high rotational bursting speed. In order to ensurelong-term operation, the friction lining is to be wear-resistant andnevertheless have good coefficients of friction.

In order to increase the bursting strength of the friction lining, it isalready known to deposit binder-impregnated strand material offriction-resistant materials, for example yarn, in a plurality of flatplies in a corrugated manner in the circumferential direction, the turnsof the strand material being guided elliptically, for example, fromoutside diameter to outside diameter forming reversal regions andkeeping the inside diameter free, the reversal regions from one turn tothe other being offset in each case at an angle over the circumference.It is therefore possible to increase the portion of strand material inthe overall composition of the friction lining and thus the friction andbursting strength of the latter. Winding usually takes place with theaid of a winding machine, one ply by definition being wound perrevolution in the circumferential direction. The number of reversalregions on the external circumference of the friction lining is referredto as the winding ratio. By way of example, a winding ratio of 1:10describes that the strand material has ten reversal regions on theexternal circumference over one circumference. Blanks wound in thismanner are pressed to their final shape in a hot-pressing process. Inorder to obtain a stable and nondeformable friction lining whichprovides the required performance, the latter is designed in anempirically determined thickness which, in addition to the frictionlayer which diminishes as a result of wear during operation, includes acarrier layer which, in particular, may have another winding beneficialfor the load-bearing capacity.

Particularly in the case of thin friction linings, the friction liningmay become warped under the action of heat. Use is therefore made ofmetal carrier sheets which, after the friction part formed from thehot-pressed blank has been produced, are adhesively bonded to thecarrier part in a plurality of process steps to form a friction lining.

It is therefore an object of the invention to propose a wound frictionlining which is easier and less expensive to produce.

This object is achieved by a friction lining, in particular for afriction clutch, comprising an annular friction part, produced at leastfrom strand material and binders, and an annular carrier part, whereinthe strand material, as a wound blank treated with binder, is subjectedto a hot-pressing process for the production of the friction part, andthe blank is pressed together with the carrier part during thehot-pressing process.

Furthermore, this object is achieved by a process for producing afriction lining comprising a wound friction part and a carrier part,having the following process steps:

-   -   binders are applied to strand material with binder,    -   a blank of strand material is wound,    -   the blank is centered on the carrier part, and    -   the blank and the carrier part are subjected to hot pressing.

The pressing of the carrier part and the friction part by thehot-pressing process eliminates the need for the complex adhesivebonding of the two parts to one another. It is therefore possible toomit working steps such as adhesive application, adhesive drying andjoining of the flashed-off parts, and also to avoid the use of adhesivematerial. A step equivalent to adhesive bonding during the hot-pressingoperation is the polymerization of components of the friction part, forexample of the binder, and this leads to a tight bond between thefriction part and the carrier part and thus replaces adhesive bonding.

The blank is advantageously formed from strand material treated withbinders. In this context, the strand material, which is optimized interms of coefficient of friction and wear, is adjusted to a constantratio of binder and strand material. By way of example, the strandmaterial may be formed from aramid fibers, glass staple fibers, viscosefibers and PAN fibers, and also brass wire or for example from glassfilaments and metal wires. The polymeric components, which experiencefurther crosslinking or polymerization during the hot-pressing process,for example by condensation reactions, addition reactions orsubstitution reactions, may consist of thermosetting components, forexample phenolic resin or melamine resin, and also elastomericcomponents, for example SBR or NBR rubber. Examples of fillers arebarium sulfate, kaolin or carbon black. The dried strand material isthen wound to form a blank.

Suitable carrier parts are stable plastics and particularly sheet metalparts. Before they are pressed together with the blank, the carrierparts are advantageously prepared for bonding thereto, for exampledegreased and/or roughened. Alternatively or in addition, the surfacefor bonding to the binder may be activated by polymerization reactions,for example polarized or treated with acid. The carrier part may bepunched from sheet metal and may have, for example, lugs with openingsto be received on flange parts of the clutch disk radially within theinternal circumference of the annular friction part. By way of example,two friction linings may be placed together on the carrier parts, withlining spring segments placed in between, and riveted to a flange partof a clutch disk. For axial securing and torsional strength, openingscan be made in the friction linings after the hot-pressing operation,and the two friction linings located opposite one another are riveted tothe lining spring segments through these openings. Since the carrierlayer produced from lining material is replaced by a carrier part madefrom sheet metal, it is possible for the wound friction lining to have asignificantly thinner design.

According to the inventive concept, friction linings produced in thisway can be further optimized by adapting the thermal coefficient of thefriction part to the expansion of the carrier part. This advantageouslytakes place in addition to the coordination of the material on the basisof the winding ratio of the blank. It has been found that thecoefficient of thermal expansion is influenced by the orientation,predefined by the winding ratio, of the friction lining surface, whichis bounded by the radius and the circumference, of the individualstrands of the strand material in the radial or circumferentialdirection. It has also been found that particularly good coordinationcan be achieved in conjunction with a carrier part of sheet metal whenthere are winding ratios between 1:2 and 1:6.

During production by the hot-pressing process, the blank isadvantageously centered on the carrier part, it being possible for thecarrier part to be positioned, for example by means of the lugs, on acharging or pressing tool at the internal circumference, and in thisrespect the blank is centered at the internal and externalcircumferences on the carrier part, such that the internal and externalradii of the friction part are flush with the carrier part.

The invention is explained in more detail on the basis of the singlefigure. This shows part of a friction lining 1 comprising a frictionpart 2 and a carrier part 3 of sheet metal as a view onto the frictionpart 2. The carrier part 3 has the same outside diameter as the frictionpart 2 and has radially inwardly expanded lugs 4 which are held on theclutch disk by means of openings 5, for example riveted to a flange partof the clutch disk with a further friction lining in a mirror-invertedmanner, with lining spring segments placed in between. The cutouts 6 inthe carrier part 3, which has preferably been punched, serve to hold thefriction linings in an elastic manner on the clutch disk, for example inorder to compensate for wobbling vibrations between the drive unit andthe transmission input shaft, on which the clutch disk is held.

The friction part 2 is held on the carrier part 3 by means of ahot-pressing process and is integrally bonded thereto by means ofpolymerization reactions of the binder. During the hot-pressingoperation, the surface shape of the friction part is predefined. Forthis purpose, it is possible, for example, to impress grooves 7 in theradial direction and/or in the circumferential direction. Two types ofcountersunk openings 8, 9 are distributed over the circumference, andthese serve to rivet two friction linings 1 arranged in amirror-inverted manner to the clutch disk, the wider openings 8 eachholding the rivet head and the openings 9 having the smaller diameterholding the rivet shafts of a clutch disk riveted on both sides.

Clutch disks equipped with these friction linings are advantageous, inparticular, for use in dual clutches for dual-clutch operations since,owing to the reduced overall axial height of the friction linings, it ispossible to use them in narrow installation spaces.

LIST OF REFERENCE NUMERALS

1 Friction lining

2 Friction part

3 Carrier part

4 Lug

5 Opening

6 Cutout

7 Groove

8 Opening

9 Opening

1. A friction lining for a friction clutch, comprising: an annularfriction part, produced at least from strand material and binders; andan annular carrier part, wherein the strand material, as a wound blanktreated with binder, is subjected to a hot-pressing process for theproduction of the friction part, and wherein the blank is pressedtogether with the carrier part during the hot-pressing process.
 2. Thefriction lining of claim 1, wherein a bond is established between thefriction part and the carrier part during the hot-pressing operation bymeans of polymerization of the binder.
 3. The friction lining of claim1, wherein a thermal coefficient of the friction part is set on the abasis of a winding ratio of the blank.
 4. The friction lining of claim3, that wherein the winding ratio is between 1:2 and 1:6.
 5. Thefriction lining claim 1, wherein the carrier part is prepared for thehot-pressing process, centered at its an internal circumference, and theblank is prepared for the hot-pressing process, positioned radially onan outside and radially on an inside and centered on the carrier part.6. The friction lining claim 1, wherein the carrier part is formed fromsheet metal.
 7. A process for producing a friction lining having a woundfriction part and a carrier part, comprising the following processsteps: applying binders to strand material; winding a blank of strandmaterial; centering the blank on the carrier part; and subjecting theblank and the carrier part to hot pressing.